1. Field of the Invention
The present invention relates to an in-plane switching mode liquid crystal display device, particularly to the in-plane switching mode liquid crystal display device of 4-pixels structure including R (Red), G (Green), B (Blue) and W (White) pixels having compensated main viewing angle to improve brightness and viewing angle characteristic.
2. Discussion of the Related Art
A light, thin, small flat panel display device have been actively studied, because such display devices may be used in various portable electronic devices such as mobile phones, PDAs (Personal Digital Assistants) and notebook computers, which have received great interest recently. An LCD (Liquid Crystal Display), a PDP (Plasma Display Panel), an FED (Field Emission Display), a VFD (Vacuum Fluorescent Display), or the like have been developed as the flat panel display device. Of these flat panel display devices, the LCD is used because of the improved mass-production technique, the simplified driving system and the high picture quality.
The LCD device has various display modes according to the arrangement of the liquid crystal molecules. Among these display modes, a TN mode (Twisted Nematic mode) LCD device is used because of good display characteristic of the white and black colors, fast response time, and low driving voltage. In the TN mode LCD device, the liquid crystal molecules arranged substantially parallel to the surface of the substrate align in the substantial vertical direction to the surface of the substrate when voltage is applied. When the voltage is applied, thus, the viewing angle is narrow because of the refractive anisotropy of the liquid crystal molecules.
To solve the viewing angle problem, LCD devices of various modes having a wide viewing angle characteristic are used, and of them, an in-plane switching mode LCD device is actually used for mass production. The IPS mode liquid crystal display device has an improved viewing angle characteristic by forming a horizontal electric field that is substantially parallel with the surface of the substrate and thus aligning the liquid crystal molecules in a plane.
FIGS. 1A and 1B show a related art IPS mode LCD device.
As shown in FIG. 1A, in the PS mode LCD device, a common electrode 5 and a pixel electrode 7 are parallel disposed on the liquid crystal display panel 1, and a rubbing direction of an alignment layer (not shown) on the liquid crystal display panel 1 is formed at a certain angle to the common electrode 5 and the pixel electrode 7. Accordingly, when a voltage is not applied to the pixel electrode 7, the liquid crystal molecules 42 are arranged in the rubbing direction to be aligned at a certain angle to the common electrode 5 and the pixel electrode 7.
When a voltage is applied to the common electrode 5 and the pixel electrode 7, a horizontal electric field that is substantially in parallel with the surface of the panel 1 is generated between the common electrode 5 and the pixel electrode 7. Accordingly, as shown in FIG. 1B, the liquid crystal molecules 42 are aligned in a direction substantially perpendicular to the common electrode 5 and the pixel electrode 7.
Namely, when the voltage is applied thereto, the liquid crystal molecules 42 are rotated in the same plane along with the horizontal electric field, and as a result a gray inversion caused by the refractive anisotropy of the liquid crystal molecules can be effectively prevented.
In the IPS mode LCD device, however, there is disadvantage in that color is shifted according to the direction of the viewing angle. Not shown in Figure, the common electrode 5 and the pixel electrode 7 are formed on a first substrate (i.e., the TFT substrate on which a thin film transistor is formed) of the liquid crystal display device. When a voltage is applied thereto, therefore, the liquid crystal molecules 42a near the first substrate are aligned to be perpendicular to the common electrode 5 and the pixel electrode 7 by the horizontal electric field, while the liquid crystal molecules 42b near a second substrate (i.e., the color filter substrate on which a color filter is formed) are aligned at a certain angle to the common electrode 5 and the pixel electrode 7. That is, the liquid crystal molecules 42a, 42b are twisted from the first substrate to the second substrate. At this time, since the liquid crystal molecules 42 are twisted in a specific direction, a color shift occurs in directions of viewing angles of X, Y as illustrated in FIG. 1(b), thereby causing deterioration of image quality.
To solve this problem, an improved IPS mode liquid crystal display device has been introduced. As illustrated in FIGS. 2A and 2B, in the IPS mode liquid crystal display device, a data line 3 is arranged at the certain angle to the gate line 2, that is, not arranged in perpendicular with the gate line 2. Further, the common electrode 5 and the pixel electrode 7 disposed in the pixel region defined by the gate line 2 and the data line 3 are disposed at a certain angle to the gate line 2, that is, the common electrode 5 and pixel electrode 7 are parallel the data line 3. In the pixel, region a common line 8 and a pixel electrode line 9, which are respectively connected to the common electrode 5 and the pixel electrode 7, are overlapped to generate the storage capacitance.
A thin film transistor 15 including a gate electrode 16, a semiconductor layer 17, a source electrode 18 and a drain electrode 19 is disposed near the crossing of the gate line 2 and the data line 3. A signal from the outside is applied through this film transistor 15 to the pixel electrode 7 to generate the horizontal electric field in the liquid crystal layer. Because the liquid crystal molecules are rotated in the same plane along with the horizontal electric field, the gray inversion caused by the refractive anisotropy can be prevented.
The related IPS mode LCD device having the above structure will be described in more detail accompanying with FIG. 2B.
As shown in FIG. 2B, a gate electrode 16 is formed on a first substrate 20, and a gate insulating layer 22 is deposited over the first substrate 20. A semiconductor layer 17 is formed on the gate insulating layer 22, and the source electrode 18 and the drain electrode 19 are formed on the semiconductor layer 17. Further, a passivation layer 24 is formed over the first substrate 20.
In addition, a plurality of common electrodes 5 is formed on the first substrate 20, and the pixel electrode 7 and the data line 3 are formed on the gate insulating layer 22, so that the horizontal electric field may be applied between the common electrode 5 and the pixel electrode 7.
On the second substrate 30, a black matrix 32 and a color filter layer 34 are formed. The black matrix 32 is for shielding the light transmitting the area where the liquid crystal molecules are not operated. The black matrix 32 is mainly formed on the thin film transistor 10 and on the area between pixels (that is, gate line area and a data line area), as illustrated in FIG. 2B. The color filter layer 23 includes R (Red), B (Blue), G (Green) colors for implementing actual colors.
A liquid crystal layer 40 is formed between the first substrate 20 and the second substrate 30.
In the related art IPS mode liquid crystal display device, the data line 3, the common electrode 5 and the pixel electrode 7 are disposed at the predetermined angle to the gate line 2. At this time, in the pixels adjacent to the corresponding pixel, especially, the pixels positioned at the upper and lower area of the corresponding pixel, the data line 3, the common electrode 5, the pixel electrode 7 are disposed at a certain angle with the gate line 2. However, these adjacent pixels are symmetric with the corresponding pixel. Accordingly, as shown in FIG. 3, the pixels are disposed in a zigzag shape in a longitudinal direction of the data line 3. In FIG. 3, we will omit the detailed structure of the IPS mode liquid crystal display device and shows only the R (Red), G (Green) and B (Blue) pixels defined by the gate line and the data line are, because each pixel has the same structure as the pixel illustrated in FIGS. 2A and 2B.
As illustrated in FIG. 3, because the R, G, B pixels are respectively formed in a zigzag shape, (i.e., the gate line and the data line are formed in a zigzag shape), a horizontal electric field is formed at each R, G, B pixels in a direction different from that of adjacent R, G, B pixels (in a symmetric direction centering around the gate line respectively). Accordingly, the liquid crystal molecules of the corresponding pixels are twisted in the opposite direction with those of the adjacent pixels from the first substrate 20 to the second substrate 30. As a result, the direction of main viewing angle becomes different in each adjacent R, G, B pixels (i.e., the viewing angles in the adjacent R, G, B pixels are symmetric centering around the gate line) to compensate the viewing angle, and thus the color shift can be prevented.
However, the related IPS mode liquid crystal display device of such a structure has following problems.
As illustrated in FIG. 3, in the related art IPS mode liquid crystal display device, the R, B pixels (R, G, B may form one pixel) are repeatedly formed over the entire liquid crystal display device (in other words, the pixel having R, G, B sub-pixels are repeatedly formed over the entire liquid crystal display device). In the R, G, B color filter layers 34 made of the color resist are respectively formed at the R, G, B pixels. Accordingly, because the light having the wave length except for the wave length of the corresponding color is absorbed in each R, G, B pixel, the intensity of light transmitting the color filter layer 34 is weakened, so that the brightness of the liquid crystal display device may be deteriorated.